Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/10—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials non-metallic substances, e.g. ferrites, e.g. [(Ba,Sr)O(Fe2O3)6] ferrites with hexagonal structure
  • H01F1/11—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials non-metallic substances, e.g. ferrites, e.g. [(Ba,Sr)O(Fe2O3)6] ferrites with hexagonal structure in the form of particles
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G49/00—Compounds of iron
  • C01G49/02—Oxides; Hydroxides
  • C01G49/06—Ferric oxide [Fe2O3]
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
  • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
  • G11B5/706—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material
  • G11B5/70626—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances
  • G11B5/70642—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances iron oxides
  • G11B5/70678—Ferrites
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/50—Solid solutions
  • C01P2002/52—Solid solutions containing elements as dopants
  • C01P2002/54—Solid solutions containing elements as dopants one element only
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/42—Magnetic properties

Definitions

• the invention relates to a process for producing cobalt-containing isotropic magnetic iron oxides of the formula (CogFe 1-x ) O (Fe 2 O 3 ] with values for x from 0.08 to 0.8 by reacting acicular r-Fe00H with divalent cobalt and Iron ions in an alkaline medium in an inert gas atmosphere.
• this magnetite is known, for example starting from ⁇ -, ⁇ - or ⁇ -FeOOH together with Fe (OH) 2 (including DE-OSen 25 08 155, 27 46 359, 25 08 085, JA-OS 36 932 ( 1983 Yale
• Fe (OH) 2 including DE-OSen 25 08 155, 27 46 359, 25 08 085, JA-OS 36 932 ( 1983
• the production of cube-shaped cobalt ferrite from cobalt hydroxide and ⁇ -FeOOH has already been described (Krause et al., Z. f. Anorg. Ch., Volume 331, page 231 (1964».
• these materials have the disadvantage that that they are not suitable for use with magnetic recording media either with regard to the magnetic properties, in particular the coercive field strength, or with regard to the stability of the magnetic properties under thermal or mechanical stress.
• the object of the invention was therefore to provide a process for the production of isotropic magnetic iron oxides which, on the one hand, can be accomplished in a simple and economical manner with common raw materials and, on the other hand, provides a magnetic material which can be obtained by isotropic magnetization, by a high coercive field strength suitable for recording media and also characterized above all by a particularly narrow switching field strength distribution of the magnetizable individual particles. These properties are particularly important for high density magnetic recording.
• the solution to this problem was the use of easily accessible iron (II) chloride as the starting material and the modification of isotropic magnetite with cobalt.
• the starting material for the process according to the invention is the acicular ⁇ FeOOH obtained in a known manner, which is also referred to as lepidocrocite, in the form of the suspension obtained in its production, the washed or unwashed filter cake or as a dried pigment.
• a further method for producing the lepidocrocite in which the nucleation by precipitation of iron (II) salt solutions with alkali or alkaline earth bases and oxidation of the iron (II) hydroxide or carbonate with oxygen, air , organic nitro compound or other oxidizing agents and optionally a growth of the lepidocrocite in iron (II) salt solutions either in the presence of metallic iron or in iron (II) salt solutions with simultaneous addition of equivalent amounts of iron (II) ions and alkali or alkaline earth metal solutions or suspensions or with simultaneous addition of equivalent amounts of iron (II) ions and alkali or alkaline earth bases, solutions or suspensions using the oxidizing agent.
• the lepidocrocite can also be obtained if a slurry of colloidal lepidocrocite seeds is produced in a first step by combining iron (II) chloride with aqueous alkali and the resulting mixture is brought to a pH with the introduction of an oxygen-containing gas. Value of the mixture stirred between 2.9 and 4.1 and then in a second stage of the slurry with vigorous stirring at a temperature of 26.7 to 60 ° C and while maintaining the pH in the presence of an excess of iron (II) chloride simultaneously and continuously alkali and an oxygen-containing gas is supplied until 1.2 to 5 parts by weight of the total product per part by weight of the seed amount have been formed.
• Suitable ⁇ -FeOOH particles can also be obtained according to DE-AS 10 61 760 or EP-A-40 722.
• an aqueous suspension of e-Fe00H is now placed in a stirred container provided with an inert gas, preferably nitrogen atmosphere.
• an Fe (II) salt solution usually FeC1 2 and at the same time or afterwards a Co (II) salt solution, usually CoCl 2
• an Fe (II) salt solution usually FeC1 2
• a Co (II) salt solution usually CoCl 2
• the reaction mixture with further stirring between 5 minutes and 8 hours, preferably between 10 minutes and 6 hours at temperatures between 35 ° C and the boiling point.
• the magnetic material obtained in this way consists of isotropic particles of the formula given.
• isotropic means that the particles are largely cube-shaped, that is to say all three spatial axes are largely large on a statistical average and that in individual terms at most length-to-thickness ratios of up to 2: 1 can be determined.
• the r-Fe00H synthesis is started in the manner described above. However, the reaction is not carried out until the end, but is interrupted after partial conversion of the Fe (II) ions, ie after the r-Fe00H nucleation phase.
• the conversion of the ⁇ -FeOOH to (CoxFe 1-x ) O (Fe 2 O 3 ) is then carried out at elevated pH values of greater than 8 to about 14, preferably 10 to 13. This is expediently carried out at temperatures between 35 ° C. and the boiling point of the suspension .. Since the reaction proceeds very quickly, reaction times of 10 minutes to 8 hours, preferably up to 6 hours, are sufficient, especially at elevated temperatures .
• the magnetic iron oxides produced according to the invention can be oxidized in a known manner with oxidizing gases, such as oxygen or air, at temperatures between 120 and 450 ° C. Depending on the respective oxidation temperature, oxidation times between 10 minutes and 6 hours have proven to be expedient.
• oxidizing gases such as oxygen or air
• oxidation times between 10 minutes and 6 hours have proven to be expedient.
• oxidation is complete, a powder composed of cobalt ferrite and co-modified gamma-iron (III) oxide is formed.
• the exact structural formula can be found here do not specify, since it cannot be determined beyond doubt how much of the cobalt (II) ions have dissolved or are included in the lattice of the gamma-iron (III) oxide phase. If the oxidation is only partial, cobalt-modified magnetite is added as the third phase.
• the magnetic iron oxides produced by the process according to the invention, can have their magnetic properties, e.g. the specific magnetization or to increase the crystallite size in a manner known per se in a reducing atmosphere, e.g. Aftertreat hydrogen and / or carbon monoxide and / or by means of organic substances which decompose in the presence of iron oxides. In order to avoid a reduction to metallic phases, the simultaneous presence of water vapor is advisable. The aftertreatment is usually carried out within 10 minutes to 2 hours at 250 to 600 ° C.
• the magnetic iron oxides according to the invention are particularly suitable from the starting material for the production of cobalt-containing iron particles, which are also used as magnetic materials in the production of magnetic recording media.
• the metal particles are produced in a manner known per se.
• isotropic magnetic iron oxides produced according to the invention are also suitable for use as printing ink pigments or for the production of magnetic toners.
• An essential use of the cobalt-containing isotropic magnetic iron oxides produced according to the invention is the use as a magnetic material in the production of magnetic recording media.
• the recording properties influenced by coercive field strength and switching field strength distribution can be surprisingly advantageously changed.
• they With their high relative remanence in all three orthogonal directions, they can be used particularly advantageously in the production of magnetic recording media with which the advantages of recording by means of the active seed vertical component to increase image density and to store high frequencies to be used.
• the recording media are produced in a manner known per se.
• the magnetic materials are dispersed in polymeric binders.
• Suitable compounds are the compounds known for this purpose, such as homopolymers and copolymers of polyvinyl derivatives, polyurethanes, polyesters and the like.
• the binders are used in solutions in suitable organic solvents, which may optionally contain further additives.
• the magnetic layers are applied to rigid or flexible supports such as plates, foils and cards.
• the present invention is illustrated by the following examples in comparison with experiments according to the prior art.
• the Co (II) or Fe (II) percentages given relate as% by weight to the total compound.
• the magnetic values of the powder samples were measured with a vibrating magnetometer at a magnetic field of 160 kA / m or after premagnetization in a pulse magnetizer in a vibrating magnetometer.
• Specific remanence (Mr / ⁇ ) and saturation (Mm / ⁇ ) are given in [nTm 3 ].
• the saturation magnetization or remanence of bands are given in [mT].
• the switching field distribution is a measure of the magnetic uniformity of an i.a. storage layer consisting of magnetizable individual particles. It specifies the magnetic field range in which the individual particles switch.
• the switching field strength distribution of a magnetic recording layer plays a decisive role in the storage of short wavelengths or high frequencies.
• a narrow SFD reduces the transition length between oppositely magnetized areas and thus allows a high recording density.
• Example 1 In the 6 1 glass apparatus described in Example 1, 150 g of f-Fe00H and 120 g of NaOH were suspended or dissolved in 3000 ml of water. The mixture was then heated to 84 ° C. within one hour with stirring. The apparatus was flushed with nitrogen during the heating process in order to create an inert gas atmosphere, which was also maintained during the subsequent steps. After the temperature had reached 84 ° C., 53.4 g of FeC1 2 and 153.4 g of CoCl 2 , both dissolved in a total of 500 ml of water, were slowly added dropwise to the ⁇ -FeOOH suspension at 84 ° C. in the course of 6 hours. Samples were taken every hour and magnetically examined. The values are given in Table 1.
• Example 2 Carried out as in Example 2/1 with the following changes: Presentation: 245 g FeCl 2 in the form of a 30.8% FeCl 2 solution and 2412 ml water. After nucleation had ended, 94.7 g of CoCl 2 .6H 2 O (dissolved in 200 ml of water) were also added. Interim samples were taken. The results are shown in Table 4.
• Example 2/1 Carried out as in Example 2/1 with the following changes: Presentation: 234 g FeCl 2 in the form of a 30.8% FeCl 2 solution and 1439 ml water. After nucleation had ended, 126.3 g of CoC1 2 .6H 2 0 (dissolved in 200 ml of water) were also added. No intermediate samples were taken. The results are shown in Table 4.
• Example 2/1 Carried out as in Example 2/1 with the following changes: Presentation: 223 g FeCl 2 in the form of a 30.8 Xigen FeCl 2 solution and 2479 ml water. After nucleation had ended, 157.9 g of CoCl 2 .6H 2 O (dissolved in 200 ml of water) were also added. No intermediate samples were taken. The results are shown in Table 4.
• each of the samples 2 / 1D, 2 / 2D, 2 / 3D and 2 / 4D were oxidized in a rotary tube furnace in an air stream of 100 Nl / h at 350 ° C. within 30 minutes.
• the measurement results of the resulting samples 2 / 1D ox to 2 / 4D ox are given in Table 4 for the starting samples.
• sample 2 / 3D 80 g were in a hydrogen stream of 50 Nl / h, which was previously passed through water at 60 ° C, for 30 minutes at 350 ° C reduced and then also oxidized for 30 minutes in an air stream of 100 Nl / h at 350 ° C.
• the measurement results of the resulting sample 2 / 3E ox are given in Table 4.
• sample 3/4 were oxidized in a rotary tube furnace with 100 N1 air / h within 30 minutes at 350 ° C. (sample 3/4 / Ox / 1).
• sample 3/4 / Ox / 1 12.5 g of sample 3/4 were also oxidized in a rotary tube furnace with 50 Nl air / h within 30 minutes at the temperatures given in table 5 (samples 3/4 / 0x / 2 to Ox / 6). The results are also shown in Table 5.
• a solution with a volume of 1500 ml was prepared from 447.75 g of FeC1 2 .4H 2 0 and water.
• 90 g of NaOH dissolved in water to a volume of likewise 1500 ml
• an air stream of 200 Nl / h was now passed through the suspension.
• the ⁇ -FeOOH nucleation had ended and the pH had dropped below 4.
• the mixture was then heated to 40 ° C. in the course of 30 minutes and, at a constant pH of 5.5, the ⁇ -FeOOH growth was initiated by adding NaOH (1400 ml of an aqueous solution of 92.4 g of NaOH) and ended after 3.75 hours.
• sample 4/4 77 g were oxidized in a rotary flask at 250 ° C. within 30 minutes with 100 N1 air / h (sample 4/2). The measurement results are shown in Table 6.
• the magnetic dispersion was filtered and then poured onto a 12 ⁇ m thick polyethylene terephthalate film using a conventional coating device, so that after drying in a drying tunnel and subsequent smoothing process with a multi-roll calender heated to 80 ° C., a layer thickness of 4.1 ⁇ m was achieved.
• the magnetic properties measured on the magnetic layer are given in Table 7.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Hard Magnetic Materials (AREA)
• Compounds Of Iron (AREA)

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• 1983
  • 1983-12-16 DE DE19833345532 patent/DE3345532A1/de not_active Withdrawn
• 1984
  • 1984-12-10 DE DE8484115034T patent/DE3472727D1/de not_active Expired
  • 1984-12-10 EP EP84115034A patent/EP0146100B1/fr not_active Expired
  • 1984-12-17 JP JP59264670A patent/JPS60151228A/ja active Granted

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